1. Field of the Invention
The present invention relates to a printed circuit board capable of preventing electromagnetic interference. More specifically, the present invention relates to a printed circuit board capable of preventing electromagnetic interference as part of the electronic circuitry, for example, a home TV game machine which is connected to other equipment by a cable and which handles high-frequency signals.
2. Description of the Prior Art
In recent years, FCC (Federal Communication Committee) regulations on electromagnetic interference have become strict in every country. One example of an apparatus which can prevent such an electromagnetic interference is disclosed, for example, in the Japanese Patent Laid-Open No. 72895/1983 laid open on May 15, 1983.
This prior art is very effective, for example, for personal computers and other self-standing equipment because a shield case is used to surround the whole unit. However, this is insufficient to prevent electromagnetic interference of home game machines, such as, the Family Computer (registered trademark). The reason is that the game machine's machine main unit is connected to other equipment, for example, a TV receiver or a controller, through a long cable. This means that the above-described prior art only prevents electromagnetic interference by confining electromagnetic energy in the shield case, is not effective in preventing electromagnetic waves radiated through the cable extending from the game machine.
In the Japanese Patent Laid-Open No. 8900/1981 laid open on Jan. 29, 1981, the Japanese Patent Laid-Open No. 20662/1984 laid open on Feb. 2, 1984, and the Japanese Patent Laid-Open No. 116437/1985 laid open on June 22, various shield plates or shield sheets are disclosed which are considered to be substitutes for the above-described shield case. However, a problem similar to that in the above-described shield case prior art remains even when such a shield plate or shield sheet is used.
In the Japanese Patent Laid-Open No. 4160/1982 laid open on Jan. 9, 1982, a semiconductor device, for example, a charge transferring device is disclosed. To prevent electromagnetic radiation from a high frequency signal generating circuit, an electric conductive layer is provided above the high frequency signal generating circuit with an insulating layer in between. This electrically conducting layer is held at a constant potential. In this prior art, electromagnetic radiation from a semiconductor chip itself is eliminated, but electromagnetic radiation from a printed pattern of a printed circuit board for mounting the chip, that is, from a signal electrode portion of the printed circuit, still can not be suppressed.